Study aims to clarify cyanide use

Canada’s 54 primary gold producers use about 23,000 tons of cyanide a year. There is emphasis on the word “about” as selling the chemical is a highly competitive business and suppliers are loathe to disclose hard figures.

Cyanamid, ICI, Du Pont and Degussa are the largest manufacturers with the first three responsible for the greater part of this country’s cyanide consumption.

But there’s more cyanide sold than that. Besides being the solvent of choice for gold and silver, electroplaters are heavier consumers, base metal miners need cyanide as a flotation conditioner and it is the starting point for a number of chemical products (for example, synthetic fibres). A broad diversified market exists.

To the general public, there are few more violent poisons. Cyanide keeps good company with arsenic and strychnine, the favorite standbys of the murder mystery writer.

Cyanide destruction is a concern of gold-mining operations. The chemical’s natural degradation is the subject of a study being undertaken by The Wastewater Technology Centre of Burlington, Ont.

When the cyanide process was first promoted in the mid-1880s as a means for extracting gold, many experts ridiculed the idea as too dangerous. Mill workers’ lives would constantly be at risk, they said.

Reality has shown that the most dangerous substances can be used in the workplace or at home, if ordinary care is taken. Cyanide is part of the normal working environment for hundreds of people across the country; gasoline, a potentially more violent substance, is commonplace and an essential part of the lives of millions.

As if to compensate for its extreme toxicity, solutions of cyanide decompose rapidly in the natural environment. Through the action of natural humic acids, bacteria and sunlight, the essential part of the cyanide converts to carbon dioxide and ammonia, both gases dispersing quickly leaving an innocuous solution behind.

A ton of clear mill solution delivered to the tailings dam contains less than 3.5 oz. cyanide (and this is an unusually strong solution to be discarded). It is little wonder that earlier mill operators directed their tailings overflow to the nearest watercourse. It was chemically harmless. Unfortunately, once the tailings pond ices over in winter, natural degradation comes to a halt.

With today’s emphasis on environmental control, most of Canada’s new gold mines have installed cyanide destruction systems. They may use sulphur dioxide, chlorine, hydrogen peroxide or other chemicals to carry out what nature can do on its own but this time under controlled conditions. According to Wastewater manager Abbas Zaidi, “there is a confusing amount of technological jargon in the business of cyanide destruction and there is the real risk of a company installing an inappropriate system.”

The Centre undertook its study to simplify the various roles natural degradation and chemical systems can play. It will be complementing this work with a study of the various competing chemical systems that are available today. A report is expected in April, 1992.

Substantial cost savings may be realized if natural and chemical degradation systems can be combined, one taking over from the other as the seasons dictate.